<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>B页面</title>
  <style>
    body {
      height: 800px;
      background-color: cadetblue;
    }
  </style>
</head>

<body>
  <p>我是B页面</p>
  <script>
    window.onmessage = function (e) {
      console.log(e.data);
      console.log(e.origin);
    }
  </script>
</body>

</html>